Former South Carolina governor Mark Sanford is trying for a political comeback after admitting an extramarital affair. / Bruce Smith, AP

by Catalina Camia, USA TODAY

by Catalina Camia, USA TODAY

Former South Carolina governor Mark Sanford vowed Wednesday to define Democratic rival Elizabeth Colbert Busch, saying the only thing voters know is that she's the sister of comedian Stephen Colbert.

"She's not held office," Sanford said in an MSNBC interview. "Stephen Colbert's a very popular, you know, well-regarded comedian but at the end of the day he's not on the ticket."

Sanford easily secured the Republican nomination Tuesday night in South Carolina's 1st Congressional District, a seat he held from 1995 to 2001 before becoming governor. Once a rising GOP star mentioned as a possible presidential candidate, Sanford left office in disgrace after admitting an extramarital affair.

The special election to replace Republican Tim Scott is on May 7.

Democrats see an opportunity in running against a Republican tainted by scandal and in a short campaign, but the district is a GOP stronghold that Mitt Romney carried in the 2012 presidential election. Sanford said on MSNBC's Morning Joe program that he'll focus the five-week campaign on issues such as the federal budget and spending, which he called "the debate of this civilization."

"We're going to have a debate on ideas," Sanford said. "I think that when people really begin to digest those ideas, some real strong contrasts in terms of where she would be vs. where I would be, I think that will substantially change a poll that I think now simply defines name ID as people know it, not issue ID."

Colbert Busch, director of business development at a former naval shipyard, said in a statement Tuesday night that she will focus on "creating jobs, balancing our country's budget and choosing an independent-minded leader who shares the values of the great people of South Carolina."

Stephen Colbert will host fundraisers for his sister on April 15 in Washington and April 23 in New York, according to a note from Colbert posted on the Democratic nominee's website. Colbert gets in a dig at Sanford, calling him "a renowned hike-lover" - a reference to Sanford saying he was hiking on the Appalachian Trail in 2009 but really visiting his mistress in Argentina.